// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_METRICS_HISTOGRAM_DELTA_SERIALIZATION_H_
#define BASE_METRICS_HISTOGRAM_DELTA_SERIALIZATION_H_

#include <memory>
#include <string>
#include <vector>

#include "base/base_export.h"
#include "base/macros.h"
#include "base/metrics/histogram_flattener.h"
#include "base/metrics/histogram_snapshot_manager.h"
#include "base/threading/thread_checker.h"

namespace base {

class HistogramBase;

// Serializes and restores histograms deltas.
class BASE_EXPORT HistogramDeltaSerialization : public HistogramFlattener {
public:
    // |caller_name| is string used in histograms for counting inconsistencies.
    explicit HistogramDeltaSerialization(const std::string& caller_name);
    ~HistogramDeltaSerialization() override;

    // Computes deltas in histogram bucket counts relative to the previous call to
    // this method. Stores the deltas in serialized form into |serialized_deltas|.
    // If |serialized_deltas| is null, no data is serialized, though the next call
    // will compute the deltas relative to this one. Setting |include_persistent|
    // will include histograms held in persistent memory (and thus may be reported
    // elsewhere); otherwise only histograms local to this process are serialized.
    void PrepareAndSerializeDeltas(std::vector<std::string>* serialized_deltas,
        bool include_persistent);

    // Deserialize deltas and add samples to corresponding histograms, creating
    // them if necessary. Silently ignores errors in |serialized_deltas|.
    static void DeserializeAndAddSamples(
        const std::vector<std::string>& serialized_deltas);

private:
    // HistogramFlattener implementation.
    void RecordDelta(const HistogramBase& histogram,
        const HistogramSamples& snapshot) override;
    void InconsistencyDetected(HistogramBase::Inconsistency problem) override;
    void UniqueInconsistencyDetected(
        HistogramBase::Inconsistency problem) override;
    void InconsistencyDetectedInLoggedCount(int amount) override;

    ThreadChecker thread_checker_;

    // Calculates deltas in histogram counters.
    HistogramSnapshotManager histogram_snapshot_manager_;

    // Output buffer for serialized deltas.
    std::vector<std::string>* serialized_deltas_;

    // Histograms to count inconsistencies in snapshots.
    HistogramBase* inconsistencies_histogram_;
    HistogramBase* inconsistencies_unique_histogram_;
    HistogramBase* inconsistent_snapshot_histogram_;

    DISALLOW_COPY_AND_ASSIGN(HistogramDeltaSerialization);
};

} // namespace base

#endif // BASE_METRICS_HISTOGRAM_DELTA_SERIALIZATION_H_
